This invention relates to a magnetic head including a reproducing head utilizing magnetoresistance effect.
Great research efforts have been made to increase the sensitivity of magnetic sensors and to increase the density of magnetic recording. One approach tends toward utilization of magnetoresistance effect wherein it is attempted to develop magnetic sensors and heads of the magnetoresistance type which are abbreviated as MR sensors and heads, respectively. Both MR sensors and heads include a reading sensor section made of a magnetic material whereby external magnetic signals are read out as resistance changes of the sensor section. The MR heads are characterized in that their reproduction outputs do not depend on the relative speed thereof to recording media and thus ensure high outputs in magnetic recording at a high linear recording density. For providing increased resolution capability and satisfactory high-frequency response, the MR heads generally include a magnetoresistance film interposed between a pair of magnetic shield components, such MR heads being known as shielded MR heads.
Japanese Patent Application Kokai (JP-A) No. 116009/1990 discloses a shielded magnetoresistance sensor which is a modification of the shielded MR head. This sensor is applicable to rigid magnetic disk storage systems or hard disk devices. In the hard disk devices, the magnetic head has an MR head exposed at the pneumatic bearing surface of a slider, permitting the MR head to be damaged by contact with the disk. More particularly, when magnetic shield films are made of a NiFe alloy or Permalloy, the shield film on the leading side (or leading shield) can be stretched by contact with the disk to form a short-circuit conductive path with the magneto-resistance film, resulting in a loss of sensor function. JP-A 116009/1990 prevents such short-circuit by using a less stretchable FeSiAl alloy or Sendust as the leading shield film.
However, Sendust film as deposited, for example, by sputtering has less desirable soft magnetic properties as compared with Permalloy. It must be annealed at temperatures above 400.degree. C. before shield properties equivalent to those of Permalloy can be exerted. Since the leading magnetic shield film is generally formed on a non-magnetic substrate or insulating film which are made of ceramic materials having substantially different coefficients of thermal expansion from Sendust, there is a likelihood for the Sendust film or insulating film to strip off upon annealing. This results in a reduced manufacturing yield.
Use of amorphous alloys as the MR head magnetic shield film is proposed in JP-B 73209/1992 and JP-A 036319/1984, 052425/1984, 090222/1984, 098318/1984, 239911/1985, and 125712/1989. However, MR heads of this type suffer from a lowering of magnetic shield performance because the amorphous alloy is degraded by heat generated by continuous current flow through the magnetoresistance film as disclosed in JP-A 258323/1986. Then JP-A 258323/1986 uses alternating films of an amorphous high permeability soft magnetic material and a crystalline high permeability soft magnetic material as the magnetic shield, which still experiences a 20% loss of magnetic permeability after 1,000 hours. Amorphous film must be heat treated at temperatures above 300.degree. C. in order to provide satisfactory soft magnetism as disclosed in JP-A 090222/1984 and 098318/1984 while such heat treatment detracts from productivity.